Servo writer heads that write servo code in one or more discrete servo bands along the entire length of a tape in a single pass are well known. The servo code is written on the tape by write elements (magnetic transducers) that are formed on the servo writer head. The write elements have a predetermined pattern such as a chevron pattern, for example. The servo bands are space apart by a pitch and areas between adjacent servo bands are reserved for uses such as data storage, for example. Typically, the servo code in at least two of the discrete servo bands is used to generate servo signals that are used to align data elements on a read/write head to a correct position for reading and writing data to one or more discrete data bands along the length of the tape. Those data bands are positioned in the area between the servo bands. The servo code is prerecorded on the tape during the manufacturing of the tape and the discrete servo bands are positioned at predetermined locations across a width of the tape. Those predetermined locations can be defined by a format specification for the tape. For instance, the format specification will determine the number of servo bands, the number of data bands, and their positions relative to one another across the width of the tape.
As more data is stored in the same amount of physical space on a tape, better reference and position accuracy is necessary. To increase the amount of data that is stored, a feature size of the write and data elements must be reduced to micron and submicron dimensions, resulting in an increase in the number of data bands that can be accommodated across the width of the tape. Servo-writing the tape requires increasingly more precision as the feature size of the write and data elements is decreased. As the servo code is written to the tape, the servo code should be centered on the patten of the write element and must be as perpendicular to a direction of tape travel as possible, for linear tape scans.
Ideally, as the tape is transported across the servo writer head, the patten for the write element should be precisely oriented with the direction of tape travel across the head. Typically, that orientation is perpendicular to the direction of tape travel. In most applications, the servo writer head is mounted in a fixture or jig such as a field replaceable unit (FRU), for example. The FRU positions the servo writer head in fixed orientation with the tape. The FRU can be designed to allow the position of servo writer head, the FRU, or both to be adjusted relative to the tape so that the servo writer head can be aligned with respect to the tape and/or the direction of tape travel.
Prior attempts to align the servo writer head include placing a visual indicator on the servo writer head. Typically, the visual indicator is placed so that it approximates the location of a magnetic axis of the servo writer head. The servo writer head is aligned by adjusting its azimuth relative to the tape until the visual indicator appears to be perpendicular to the direction of tape travel or perpendicular to one or both of the tapes edge's. Methods for forming the visual indicator include marking the servo writer head with a tool to form the visual indicator. For instance, a scribed mark (an incised mark) can be used to form the visual indicator.
Referring to FIGS. 1a and 1b, a prior art tape head 200 includes one or more write transducers 241 positioned along a magnetic axis 250 of the tape head 200. A tape 220 having opposed edges 221 and 223 is in contact with the tape head 200 and is transported across the tape head 200 in a direction of transport D. A visual indicator 215 is formed on the tape head 200 and is operative to define a gross point of reference on the tape head 200. Typically, the visual indicator 215 defines the approximate location of the magnetic axis 250. The position of the tape head 200 is adjusted 251 relative to the tape 220 until the visual indicator 215 appears to be approximately perpendicular to the direction of transport D as shown by angle α, which represents an angle that is approximately 90 degrees. One disadvantage of the visual indicator 215 is that its location on the tape head 220 is only an approximation of the gross point of reference i.e. the magnetic axis 250. Because the visual indicator 215 is formed on the tape head 200 after the tape head 200 has been manufactured, it is extremely difficult if not impossible to precisely align the visual indicator 215 with the magnetic axis. Therefore, an axis 217 through the visual indicator 215 will not be colinear with the magnetic axis 250 thereby resulting in the magnetic axis 250 having an orientation angle α3 that is not perpendicular to the direction of transport D (i.e. α3≠90 degrees). It is far more likely that the axis 217 will displaced from the magnetic axis 250 (see FIG. 1b) and be anti-parallel to the magnetic axis 250. Consequently, the visual indicator 215 is not an accurate indicator that can be used for precision alignment of the write transducers 241 with the direction of transport D. Moreover, if the write transducers 241 have feature sizes that are in the micron or submicron range, then even the slightest alignment error caused by the visual indicator 215 can result in a substantial misalignment of the write transducers 241 with the direction of transport D.
Prior attempts to align the servo writer head have also included using opposing sides of the servo writer head to align the servo writer head with the tape. This approach assumes that the opposing sides of the servo writer head were manufactured such that the opposing sides are parallel with each other and are parallel and/or perpendicular to the magnetic axis of the servo writer head. However, in reality, the servo writer head may be cut using a saw blade or the like. As a result, the opposing sides will not be exactly parallel to each other. For example, instead of having a rectangle shape, the servo writer head will have a parallelogram shape.
Referring to FIGS. 2a and 2b, a prior art tape head 300 includes opposing sides 301 and 303 that are not parallel to each other and are not parallel to or perpendicular to a magnetic axis 350 of the tape head 300 (i.e. the tape head 300 has a non-rectangular shape). The tape head 300 includes one or more write transducers 341 positioned along the magnetic axis 350. A tape 320 having opposed tape edges 321 and 323 is in contact with the tape head 300 and is transported across the tape head 300 in a direction of transport D. A side axis 305 on opposed edge 301 is adjusted 351 until it appears that either one or both of the opposed sides 301 are perpendicular with either one or both of the opposed tape edges (321 and 323) as indicated by an angle α2 in FIG. 2b. However, because the opposed sides 301 are not parallel to each other, the magnetic axis 350 is not perpendicular to the direction of transport D when it appears that angle α2 is perpendicular to the tape edges (321 and 323). It should be noted that this is due in part by the side axis 305 not being parallel to the magnetic axis 350. Consequently, the magnetic axis 350 makes an angle α4 that is not perpendicular to the direction of transport D (i.e. α4≠90 degrees) when the side axis 305 is at the angle α2. Similarly, if opposing sides 303 are use to align the tape head 300 so that either one of the opposing sides 303 are parallel to either one or both of the opposed tape edges 321 and 323, the magnetic axis 350 will not be perpendicular to the direction of transport D when it appears that the opposing sides 301 are parallel to the tape edges (321 and 323). Therefore, if the magnetic axis 350 is not perpendicular to the direction of transport D, then the write transducers 341 are also not perpendicular to the direction of transport D.
In servo write head applications, the aforementioned alignment problems can result in azimuth errors in the servo code written onto the tape during manufacturing. For instance, in the Liner Tape Open format, the servo code is written on the tape in five bands. Alignment of the data head to the tape is achieved by using a band-to-band alignment between adjacent servo bands. The servo code in those adjacent servo bands is used to derive a position signal that is an average of the servo code in the adjacent bands. When the write transducers of the servo write head are not aligned with the direction of transport, the servo code in one of the adjacent servo bands will be written on the tape earlier than the servo code in another adjacent servo band (i.e. when viewed on the tape, one servo band will appear to be written earlier than the other servo band). Consequently, the servo code in the adjacent servo bands has a built-in azimuth error that skews (an inter band skew) the averages that are used to derive the position signal. The inter band skew can result in a band ID failure or the inter band skew can result in a longer time for the data head to position itself.
As was mentioned above, the decreasing feature size of the transducers requires greater alignment accuracy than can be achieved using the above mentioned prior art techniques. For instance, in same-surface-servo applications in which the servo code is prerecorded on the tape prior to data being written to or read from the tape, it is important that the servo code be precisely aligned with the tape such that the servo band is parallel to the direction of tape travel and the servo code is aligned perpendicular to the direction of tape travel. If the servo code is not precisely aligned with the tape, then the servo code can occupy and/or interfere with the data in adjacent data bands. Because the servo code is prerecorded on the tape before the data is written to the tape, the resulting misalignment can not be corrected after the tape has been manufactured. Therefore, it is essential to address precision alignment during the manufacturing process.
Therefore, there exists a need for precision alignment of a write element on a tape head with a transport direction of a tape that is transported across the tape head. Furthermore, there exists a need to precisely align a write element on a tape head with a transport direction of a tape that is transported across the tape head so that inter band skew is significantly reduced or eliminated. There also exists a need for gross alignment of the write element with the transport direction of the tape that is not dependent on opposing sides of the tape head being parallel or on physically marking the tape head. Finally, there is a need to align a tape head that reads and/or writes data to a tape with a transport direction of the tape.